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LM2623 数据表(PDF) 10 Page - Texas Instruments |
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LM2623 数据表(HTML) 10 Page - Texas Instruments |
10 / 21 page SW 4.7pF C3 4.72H L1 FREQ 7 2 6 4 8 3 1 PGND SGND BOOT EN FB D1 3A 5V RF2 100k C1 222F V IN 2 Cells R3 150k RF1 300k + V DD LM2623 C2 1002F tant 5 LM2623 SNVS188H – MAY 2004 – REVISED NOVEMBER 2014 www.ti.com 8 Applications and Implementation NOTE Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality. 8.1 Application Information The LM2623 features a shutdown mode, entry into the shutdown mode is controlled by the active-low logic input pin EN (pin 2). When the logic input to this pin is pulled below 0.15 VDD, the device goes into shutdown mode. The logic input to this pin should be above 0.7 VDD for the device to work in normal start-up mode. 8.2 Typical Application Figure 9. LM2623 Typical Application 8.2.1 Design Requirements The LM2623 allows the designer to vary output voltage, operating frequency and duty cycle to optimize the part performance, please read Detailed Design Procedure for details. 8.2.2 Detailed Design Procedure 8.2.2.1 Non-Linear Effect The LM2623 is very similar to the LM2621. The LM2623 is based on the LM2621, except for the fact that the LM2623 takes advantage of a non-linear effect that allows for the duty cycle to be programmable. The C3 capacitor is used to dump charge on the FREQ pin in order to manipulate the duty cycle of the internal oscillator. The part is being tricked to behave in a certain manner, in the effort to make this Pulse Frequency Modulated (PFM) boost switching regulator behave as a Pulse Width Modulated (PWM) boost switching regulator. 8.2.2.2 Choosing the Correct C3 Capacitor The C3 capacitor allows for the duty cycle of the internal oscillator to be programmable. Choosing the correct C3 capacitor to get the appropriate duty cycle for a particular application circuit is a trial and error process. The non- linear effect that C3 produces is dependent on the input voltage and output voltage values. The correct C3 capacitor for particular input and output voltage values cannot be calculated. Choosing the correct C3 capacitance is best done by trial and error, in conjunction with the checking of the inductor peak current to make sure your not too close to the current limit of the device. As the C3 capacitor value increases, so does the duty cycle. And conversely as the C3 capacitor value decreases, the duty cycle decreases. An incorrect choice of the C3 capacitor can result in the part prematurely tripping the current limit and/or double pulsing, which could lead to the output voltage not being stable. 10 Submit Documentation Feedback Copyright © 2004–2014, Texas Instruments Incorporated Product Folder Links: LM2623 |
类似零件编号 - LM2623_15 |
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类似说明 - LM2623_15 |
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